MAKING WAVE ENERGY DURABLE

On the Crest of Wave Energy: An aerospace approach
November 19, 2009 (Scientific Computing)

"The ocean is a potentially vast source of electric power, yet as engineers test new technologies for capturing it, the devices are plagued by battering storms, limited efficiency and the need to be tethered to the seafloor. Now, a team of aerospace engineers is applying the principles that keep airplanes aloft to create a new wave-energy system that is durable, extremely efficient and can be placed anywhere in the ocean, regardless of depth.

"While still in early design stages, computer and scale-model tests of the system suggest higher efficiencies than wind turbines. The system is designed to effectively cancel incoming waves, capturing their energy while flattening them out, providing an added application as a storm-wave breaker… [lead researcher Stefan Siegel and his team from the U.S. Air Force Academy] developed a system that uses lift instead of drag to cause the propeller blades to move [with sensors and adjustable parts to control how fluids flow around airfoils like wings]…"

Blades turned vertically. (click to enlarge)

"Windmills have active controls that turn the blades to compensate for storm winds, eliminating lift when it is a risk, and preventing damage. The Air Force Academy researchers used the same approach with a hydrofoil (equivalent to an airfoil, but for water) and built it into a cycloidal propeller, a design that emerged in the 1930s and currently propels tugboats, ferries and other highly maneuverable ships.

"The researchers changed the propeller orientation from horizontal to vertical, allowing direct interaction with the cyclic, up and down motion of wave energy. The researchers also developed individual control systems for each propeller blade, allowing sophisticated manipulations that maximize (or minimize, in the case of storms) interaction with wave energy."

A look under wave energy's hood. (click to enlarge)

"…[T]he goal is to keep the flow direction and blade direction constant, cancelling the incoming wave and using standard gear-driven or direct-drive generators to convert the wave energy into electric energy. A propeller that is exactly out of phase with a wave will cancel that wave and maximize energy output…[and allow] the float-mounted devices to function without the need of mooring, important for deep-sea locations that hold tremendous wave energy potential and are currently out of reach for many existing wave energy designs.

"While the final device may be as large as 40 meters across, laboratory models are currently less than a meter in diameter. A larger version of the system will be tested next year at…Oregon State University…"